- The US government went into shutdown in the absence of an agreed budget
- Under a shutdown, federal services come to a halt or are scaled back
- Donald Trump has blamed the shutdown on the Democrats
As the clock struck midnight, in the absence of an agreed spending plan, federal services began to come to a halt or be scaled back.
Essential services and military activity will continue but many public sector workers will be sent home without wages and even serving soldiers will not be paid until a deal is reached to reopen the US government.
"Democrats are far more concerned with Illegal Immigrants than they are with our great Military or Safety at our dangerous Southern Border," Mr Trump wrote in an early morning tweet.
"They could have easily made a deal but decided to play Shutdown politics instead. #WeNeedMoreRepublicansIn18 in order to power through mess!"
"This is the One Year Anniversary of my Presidency and the Democrats wanted to give me a nice present," he added.
Vice President Mike Pence had earlier raised the issue of soldiers' salaries after meeting with US military personnel on a stopover in Shannon Airport in Ireland ahead of a three-country tour of the Middle East.
"You have troops headed down range to Kuwait for six months and they are anxious about the fact that they aren't going to get paid right away," he told reporters. "It's unconscionable."
A deal had appeared likely on Friday afternoon, when Mr Trump seemed to be close to an agreement with Democratic Senate minority leader Chuck Schumer on a measure to prevent the expulsion of undocumented migrants who arrived in the country as children.
But no such compromise was in the language that reached Congress for a stop-gap motion to keep the government open for four more weeks while a final arrangement is discussed and Republicans failed to win enough Democratic support to bring it to a vote.
The White House lashed out at Schumer, blaming him for the shutdown and doubling down: Mr Trump's spokeswoman Sarah Sanders declared that he would never negotiate an immigration deal until Congress agrees to resume normal government spending.
"Senate Democrats own the Schumer Shutdown," she declared.
"We will not negotiate the status of unlawful immigrants while Democrats hold our lawful citizens hostage over their reckless demands," she said.
Republican majority leader Mitch McConnell echoed the White House's language, but Schumer fought back, blaming Mr Trump for leading him to believe a deal was possible on the immigration dispute but then failing to bring his own party along.
Responsibility to govern
"Every American knows the Republican Party controls White House, the Senate, the House -- it is their job to keep the government open. It is their job to work with us to move forward," Schumer told the Senate, after the 50 to 49 vote.
Schumer added he had also offered to discuss the possibility of building a wall along the border with Mexico, a key campaign pledge made by Mr Trump that is anathema to many Democrats.
"Even that was not enough to entice the president to finish the deal," he said.
Democrats accused Republicans of poisoning chances of a deal and pandering to Mr Trump's populist base by refusing to fund a program that protects 700,000 "Dreamers" -- undocumented immigrants who arrived in the US as children -- from deportation.
The president shelved plans to fly to Florida to celebrate at his Mar-a-Lago estate the first anniversary of his inauguration to remain in Washington to ride out the storm.
Republicans have a tenuous one-seat majority in the Senate but would have needed to lure some Democrats to their side to get a 60 vote supermajority to bring the motion forward. They fell ten votes short.
The measure brought to Congress would have extended federal funding until February 16 and reauthorized for six years a health insurance program for poor children -- a long-time Democratic objective.
But it would have cut the Deferred Action on Childhood Arrivals program, known as DACA, that affects Dreamers.
White House officials insisted there was no urgency to fix DACA, which expires March 5.
There have been four government shutdowns since 1990. In the last one in 2013, more than 800,000 government workers were put on temporary leave.
International ratings agency Fitch said a partial shutdown was unlikely to affect America's AAA/stable rating for US sovereign debt.
Negotiations with the White House on a bipartisan compromise on DACA blew up last week after Mr Trump reportedly referred to African nations and Haiti as "shithole countries."
The Senate was set to reconvene at noon on Saturday, with McConnell seeking a new stop-gap measure to fund the government till February 8.